The invention relates to a plastics nut for turning onto a threaded stud, particularly a weld stud, and having a smooth bore extending from an inwardly-tapering conical lead-in area.
Plastics nuts such as collar nuts or cap nuts are known which may be turned onto a threaded stud and are provided with a smooth internal bore extending from an inwardly-tapering conical lead-in portion. When such a nut is turned onto a threaded stud, a thread is formed in the bore of the nut. Such a collar nut is described in German Patent specification DE 28 02 465. This discloses a collar nut which is further provided with axial grooves in order to displace any material cut away by the formation of the thread in the bore of the nut and occasional paint residues left on the thread of the stud.
The stud may, however, be subjected to more than occasional residues so that it is heavily coated with paint or other surface treatment agents. For example, motor car bodies are treated to inhibit rust (undersealing) usually after the threaded studs have been welded to the untreated vehicle body. Many problems arise if a plastics nut is screwed onto a threaded stud coated wholly or partly with paint or underseal material. The thread formed in the bore of the nut may be imperfect and an increased torque must be applied to the nut in order to form the internal thread.
The quantity of the underseal coat inevitably varies from stud to stud so that the torque required to tighten each nut varies and this is not a welcome requirement on an assembly line, particularly an automated assembly line. Furthermore, the torque required may exceed a pre-set torque limit so that screwing is terminated before the nut is screwed fully home and the nut may not abut the component to be secured by the screw. Additionally, imperfect thread formation in the bore of the nut may affect the friction values between the nut and the threaded stud in an unacceptable way.
A collar nut to overcome these problems is described in our German Gebrauchsmuster G84 175 583 wherein a component is provided with a bore and can be turned onto a threaded stud sprayed with a tough coating. The bore is provided with a smooth inner wall and with a substantially conical lead-in area, sharp-edged projections being provided within the lead-in area for removing the coating when being screwed on, these projections being directed toward the axis of the weld stud and extending radially generally up to the diameter of the bore.
The invention relates to a stripping nut for turning onto a threaded stud which has a simplified design making manufacture easier and cheaper whilst achieving the effectiveness of the nut described above.